Can I render an image along the X axis - so it's completely flat? or not
Select the camera and click the camera tab of the Properties Window.

Then under lens change the type from perspective to orthographic and adjust the orthographic scale to fit your scene.

Now you can press N  to adjust the location and rotation.
These settings should get you where you want to be:


Location: (10, 0, 0)
Rotation: (90, 0, 90)